Ever since farm machinery or implements were developed to cover a wide swath, attempts have been made to have the machines follow the contours of the ground, which in many areas undulates to various degrees. Very early, as shown, for example, in U.S. Pat. Nos. 2,641,886, 3,321,028 and 4,133,391 machines were proposed with hinged side-by-side frame sections to follow ground contours and also allow folding for transport. These machines, though they could only flex about their hinge axes generally parallel to the direction or path of travel, proved to be a big improvement over rigid frame machines. Hinged sectional-frame tillage implements also have been proposed to allow frames to flex about at least two angularly-divergent axes by having the several hinge axes arranged at various different angles relative to travel direction. This is shown, for example, in U.S. Pat. No. 3,487,882. This implement, however, cannot fold compactly. Further, even though that implement provides axes of flexibility at different angles, very often an individual flex axis will not match the contour of the ground.
Other highly flexible machines have been proposed which use a wide span hitch or drawbar to tow many small identical modular operational units, e.g., drills, as shown, for example, in U.S. Pat. No. 4,109,928. In that machine, each independent unit follows the ground contours of a narrow portion of the entire swath. This arrangement cannot be folded for transport, however, and requires an expensive hitch or drawbar which must be built with a strength comparable to that of the towed tillage units. In contrast to the machine of U.S. Pat. No. 4,109,928, cost efficient tillage equipment mounts tillage tools on a hitch type structure in which the frame serves a dual purpose.
Still other machines have been proposed that improve on hitches which tow identical operational units that independently follow ground contours. For example, U.S. Pat. No. 4,191,260 discloses a tow hitch with which it is possible to fold the individual operational units for transport. However, this structure is very complicated and, accordingly, expensive to build.
There are still other flexible improvements in wide-swath machines, such as those shown in U.S. Pat. Nos. 4,355,689 and 4,105,077, wherein the machines flex about their folding axes. While these machines have a high degree of flexibility and are less expensive to build than other machines of comparable flexibility, they allow flexing only about hinge axes parallel to travel direction and the folding mechanisms are very complex, particularly that disclosed in U.S. Pat. No. 4,355,689. Such complex folding mechanisms are not only expensive but also not entirely trouble free.